TABLE 1.

Table used to calculate the sensitivity, specificity, PPV, and NPV of a testa

ResultDiseaseNo disease
PositiveTrue positive (a)False positive (b)
NegativeFalse negative (c)True negative (d)
• a Sensitivity is the proportion of people with disease in whom the test result is positive [a/(a + c)]. Specificity is the proportion of people without disease in whom the test result is negative [d/(b + d)]. PPV is the proportion of people with a positive test result who have disease [a/(a + b)] or (sensitivity × prevalence)/{(sensitivity × prevalence) + [(1 − specificity) × (1 − prevalence)]}. NPV is the proportion of people with a negative test result who do not have disease [d/(c + d)] or [specificity× (1 − prevalence)]/{[(1 − sensitivity) × prevalence] + [specificity × (1 − prevalence)]}.